Sunday, June 16, 2013

Here is a description of the process for making a rubber glove mold with a fiberglass mother mold. I tried to make it as clear as possible but if you have any questions or suggestions about how to make it easier to understand please let me know.

Mold making steps for back to back
silicon rubber glove mold with fiberglass mother

Always be sure to read the manufacturer’s
product safety warnings and handling directions when using any of the materials
or tools mentioned in this article.

Be sure the rubber
won’t stick to your pattern.If the
pattern you are using is made of a porous material such as plaster or fired
clay you need to paint it with a solution of Vaseline and mineral spirits. This
solution will work as a release agent. If the pattern is made of wet clay or
oil based clay the rubber will not stick.However the chemical composition of some clay bodies may contain
chemicals which will inhibit the curing of the rubber. If you aren’t sure that
the rubber will cure against the clay you are usingyou should test it on a small section of your
pattern or on another sample of the same clay. If the rubber doesn’t cure
within a day you will need to seal the pattern with shellac before you apply
the rubber to it.

Steps in making the mold:

1.If the pattern is loose attach it firmly to a
plywood base. Paint a coat of Vaseline on the surface of the base.This will prevent the rubber glove mold and
the fiberglass and polyester mother mold from sticking to the base.

2.Prepare the brush coat.Do this is a well ventilated area, preferably
outdoors. This coat of rubber is made by mixing DOW 700 clear caulking rubber
with an equal amount of xylene or xylol.The cups used to mix polyester resins will work for preparing the brush
coat.Squeeze an appropriate amount of
rubber out of the caulking tube into the plastic cup. Add the xylene and mix
until the mixture has the consistency of honey at room temperature.Using a china bristle brush, paint a thin
coat of the rubber solution onto the pattern. Do not allow it to form deep
pools.Allow the solution to cure. This
will take about 24 hours.

3.After the brush coat has cured it will still
feel very slightly tacky to the touch. Using a painter’s palette knife carefully
apply as even a coat of the DOW 700cl as evenly as possible to the surface of
the pattern.Allow this 2nd
coat to cure 24 hours. Work from the wet areas into the dry areas, pushing the
rubber ahead with the back edge of the blade so that you do not include air and
leave bubbles in the rubber.

4.Build a parting line on the patter using shims
made from waxed paper cups.These cups
must have a waxy coating on the surface or else the rubber will stick to
them.Cut the shims to conform to the
profile of the pattern along the line on which you want to build your parting
line.

Attach them to the pattern using straight
pins to both hold them to the pattern and to each other.

After
you have constructed the parting line use a paper punch to put holes through it
where you want to place your keys*.

Squeeze a ribbon of rubber from the
caulking tube onto the conjunction of the base of the shims and the
pattern.Do this on both sides of the
shims.

Wait 1 or 2 hours and then place your
rubber keys through the holes in the shims.

Put
all the stops of the keys on one side of the shim and the nipple end of the key
through to the other side of the shim.Paint Vaseline on the nipple end of the keys and the exposed parts of
the steel pins holding the shims to the pattern.Be sure not to get any Vaseline on the back
of the keys.

Next, using a palette knife, spread a layer of rubber over the back of the
shims on the other side; take care to cover the back of the keys with rubber as
you do this so that they will be firmly attached to the parting line on that
side of the shim.

Allow this to cure for
24 hours.

5.Paint a second coat of Vaseline onto the
nipples.Next squeeze a layer of rubber
onto the side of the shim with the nipple protruding. Be sure to cover the
nipples completely with rubber. Allow to cure 24 hours.

6.Remove the straight pins. You may need to leave some pins in the outboard edges of the shims to hold them together there. Apply a third layer of rubber with the palette knife. As you are doing this embed a double layer of
cheesecloth into the rubber.

This cheesecloth will provide much greater
tear strength than the rubber has by itself.

Squeeze a bead of rubber onto the pattern
and then spread it out onto the surface with the palette knife. Next place an
appropriate sized and shaped piece of cheesecloth onto this rubber bed and then
squeeze a bead of rubber onto the top of the cheesecloth.Use the palette knife to work the rubber into
the cheesecloth until it is entirely involved in the rubber. Be sure to push
the cheesecloth into the deepest recesses first and then work out to the higher
areas. Be careful not to create any holes under the surface of
the rubber by allowing the cheesecloth to bridge from one high spot to another
high spot. Always push the cheesecloth firmly into contact with the previous
coat of rubber.Allow 24 hours to cure.

When you have finished run a bead of rubber
around the edges of the shim on both sides. This will make the outboard edges
of the shim stronger and more difficult to tear. It will also create a dam
which will help contain the edge of the fiberglass and polyester resin when you
make the mother mold.

7.Make the smooth coat.This
coat will create a smooth surface on the rubber mold that will easily separate
from and then fit back into the mother mold.The objective is to create as smooth and regular a surface as possible. Squeeze
a concentric bead of rubber onto the pattern about ¾ “ between passes.Immediately use the palette knife to spread
the rubber as evenly as possible all over the surface of the pattern. Put on a pair of latex rubber gloves and then
dip your hands in a solution of detergent and water. Use about ¼ cup of
detergent to 1 qt of water. This solution will prevent the rubber from sticking
to your latex gloves as you smooth the surface of the rubber with your hands.
If the rubber begins to stick to your gloves add more detergent until it no
longer sticks. Allow to cure 24 hours.

8.Make the mother mold. Be sure each side of the
mold has a “clean draft”, that is that there are no deep holes or areas that
will create a mechanical lock in the rigid mother mold and prevent it from
releasing from the pattern.If there are
places on the surface that will create a mechanical lock you can correct the
problem by filling them with clay.

When you can see the entire surface of the
area on which you will be making the mother mold from one view point then there
will be no mechanical locks.Cut fiberglass mat into appropriate sized
pieces.Lay them out so they will be
easy to pick up. In a well ventilated area pour about 4 liquid oz. of polyester
resin bond coat into a plastic container and then mix 7 to 10 drops per ounce (depending
on the temperature and humidity) of catalyst into the resin.

Stir thoroughly and then use a china
bristle brush to paint a coat of the catalyzed resin onto the surface of the
rubber.

While it is still tacky stick pieces of the
fiberglass mat onto the surface and paint it down onto the surface of the
rubber.

Be sure to work the mat into the deep areas
first and work out to the tops of the higher areas and ridges last. Apply 2 to
4 layers of mat in this way. After the resin has cured hard use a side grinder
with an abrasive disc to lightly sand away any pieces of fiberglass that are
protruding from the surface of the mold creating sharp areas. Mix up a final
coat of resin and catalyst and finishing wax and paint it onto the surface of
the mold.Allow to cure 4 or 5 hours.

9.Using a 5/16” drill bit drill holes through the
fiberglass and rubber shims in enough places that will insure you will be able
to secure the parts of the mold together after you have removed the pattern.

10.Separate the mold and remove the pattern.Using a putty knife gently work the blade in
between the rubber and the fiberglass mother mold and force it away from the
rubber.

Once you have removed the mother mold from
the rubber use your side grinder to clean up the outboard edgesso that you can handle it without cutting or
puncturing your hands.Next force your
blade between the two sides of the rubber shims and separate them as much as
possible along the whole shim line. Remove the paper cup shim stock from
between the sides of the rubber shim.

Using a razor blade cut through the 1st
and 2nd layers of rubber on which the shims are built to the surface
of the pattern. Once the parting line has been opened up to the surface of the
pattern you should gently begin pulling the rubber away from the pattern. Do
not pull it away quickly or violently, rather proceed cautiously so as not to
tear the rubber in the recesses away from the rest of the rubber mold.

11.Once the rubber is off of the pattern clean it
thoroughly and then put it back into the fiberglass mother mold.Use 1/4” bolts and wing nuts to secure the
two sides of the mold together when you reassemble it.

The mold is now ready to use.

Making the rubber keys

1.Make a ¼” by 18” bead of rubber on a sheet of
waxed paper and let it cure for 24 hours

2.Cut the rubber bead in ¼” to 3/8” long segments.

3.Press the tip of the caulking gun against a
sheet of waxed paper and make a series of shallow discs or pats of rubber.

4.Stick one end of each segment into a pat of
rubber while the pat is still wet. This will create a flange on the end of each
segment which will work as the stop on the back of the key when you push it
through the holes in the paper shims you have attached to the pattern in step 4
above. Allow the keys to cure over night. You can easily make several hundred
keys at a time in this way.

Monday, June 3, 2013

I want to use this blog to communicate with friends, students, customers and anyone else interested in making sculpture. I'll put up images of things I am working on and hopefully we can get images posted of work by other artists. I look forward to discussing technical issues and have some articles in mind on mold making and foundry practices I want to write and publish here. This blog will be linked to my facebook page, youtube, and my website. Several viewers of the tutorial videos on making a clay portrait head have written posted questions there about the materials and techniques shown in the videos. I will be able to give more complete answers here on the blog that I can on youtube. It will also be a good place to collect information on questions about techniques and materials for making sculpture from other sculptors.

This is my first attempt at making a blog, I expect that my approach will change a lot as I figure out how to go about it in the most fun and effective way.

Here are a couple of pieces I just put up on facebook today. the one on top is about 31" tall and made of bronze. The one on the bottom I will be casting in paper. I made it last night and will start molding it later today. I'll put photos of the process up here on the blog.